Pulp molding

ABSTRACT

A pulp molding is formed by molding a feedstock consisting of, as principal components, pulp and some binder. The feedstock contains plastic microspheres which form uniformly distributed voids in the pulp molding. The pulp molding has cushioning characteristics higher than those of the conventional pulp molding and equivalent to those of a foam styrene board, and moisture absorbing characteristics lower than those of the conventional pulp molding. The pulp molding can be deflocculated in water for reclamation without causing environmental pollution.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pulp molding and, more particularly,to a pulp molding alternative to foam styrene resin materials.

2. Description of the Related Art

Packings of foam styrene resin having excellent cushioningcharacteristics have been used in packing electric apparatus includingtelevision sets and video tape recorders. However, environmentalpollution attributable to waste packings of foam styrene resin havebecome a serious problem because foam styrene resin is unperishable andundecomposable in soil and produces noxious gases when incinerated.Accordingly, the development of pollution-free packing materialsalternative to foam styrene resin packing materials has been desired.One of the remarkable alternative packing materials is a pulp moldingformed by molding a feedstock produced by processing waste paper, suchas newspaper, as a principal raw material, and pulp packings formed bymolding pulp materials have been used for packing small electricapparatus including cassette tape recorders.

A pulp molding currently used as a pulp packing contains, as principalcomponents, pulp and a vinyl acetate copolymer containing ethyleneserving as a synthetic binder. This vinyl acetate copolymer is usedwidely for paint and adhesives. The material of the pulp moldingcontains the synthetic binder to enhance the water resistance of thepulp molding. Generally, the pulp molding contains 8% by weightsynthetic binder. However, the cushioning property of the pulp moldingformed of the conventional material is not sufficiently high and such apulp molding is not suitable for packing large electric apparatusincluding television sets and video tape recorders.

If the vinyl acetate resin content of the pulp molding is 8% by weightto reduce the hygroscopicity of the pulp molding, it is difficult todeflocculate the pulp molding for reclamation because the binder isdifficult to resolve in water. Furthermore, the effect of the binder onthe reduction of the hygroscopicity of the pulp molding isinsignificant; for example, while the moisture percentage of a pulpmolding not containing any binder is 10.8% when the same is kept for apredetermined time in an environment of a temperature of 60° C. and arelative humidity of 80%, the moisture percentage of the pulp moldingcontaining 8% by weight binder kept in the same environment is 9%. Thus,the physical properties of the pulp molding are liable to deteriorate ina high-temperature high-humidity environment.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a pulpmolding having satisfactory cushioning characteristics and a lowhygroscopic property and capable of being readily processed forreclamation without entailing environmental pollution.

A pulp molding in one aspect of the present invention is formed bymolding a feedstock containing pulp as a principal component, a smallquantity of binder, and plastic microspheres.

Preferably, the feedstock contains additives of a pulp plasticizer androsin size.

Furthermore, preferably, the binder is a polymer emulsion and a watersoluble bio-degradable.

The feedstock containing pulp as a principal component, a small quantityof binder and the heat-expandable microcapsules is molded to obtain, forexample, a pulp packing material. When heated at a high temperature, theheat-expandable microcapsules formed of a polymer soften, and thehydrocarbon contained in the heat-expandable microcapsules gasifies andthe heat-expandable microcapsules expand in a volume several tens timesthe initial volume thereof. The expanded heat-expandable microcapsuleshave a specific gravity of 0.5 or below and is capable of elasticdeformation. Accordingly, voids can be formed in the pulp molding whenthe feedstock contains only a small quantity of the heat-expandablemicrocapsules and the voids formed in the pulp molding absorb shocks,which invests the pulp molding with improved cushioning characteristics.

The pulp plasticizer, such as glycerol, improves the cushioningcharacteristics of the pulp molding.

The binder such as chitosan improves the mechanical properties of a pulpmold. The rosin size added to the feedstock reduces the hygroscopiccharacteristic of the pulp mold. The rosin size is produced by synthesisusing natural colophony as a raw material. Therefore, the rosin size, ascompared with the synthetic vinyl acetate binder, is less pollutive tothe environment. Since the rosin size is not a synthetic resin, the pulpmolding containing the rosin size can be deflocculated in water forreclamation and hence the pulp molding will not entail environmentalpollution.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description takenin connection with the accompanying drawings, in which:

FIG. 1 is a graph showing the measured variation of compressive stresswith compressive deformation ratio for pulp moldings formed offeedstocks differing from each other in composition in a firstembodiment according to the present invention;

FIG. 2 is a graph showing the measured variation of compressive stresswith compressive deformation ratio for pulp moldings in the firstembodiment according to the present invention and comparative examples;

FIG. 3 is a graph of assistance in explaining the definition of Ee andEp in the first embodiment;

FIG. 4 is a typical view showing the state of a test piece of a pulpmolding in the first embodiment after compression at a compressivedeformation ratio of 75%;

FIG. 5 is a typical view showing the state of a test piece of a pulpmolding in the first embodiment after compression at a compressivedeformation ratio of 75%;

FIG. 6 is a view showing the classification of sizes contained infeedstocks for forming pulp moldings in a second embodiment according tothe present invention;

FIG. 7 is a graph showing the measured variation of compressive stresswith compressive deformation ratio for pulp moldings in a thirdembodiment according to the present invention; and

FIG. 8 is a graph showing a stress-strain curve for the pulp moldings inthe third embodiment according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

A material for forming pulp moldings in the first embodiment includes apulp slurry a solid content of 24% as a principal component, a vinylacetate emulsion as a binder, and heat-expandable microcapsulescontaining an organic solvent having a low boiling point (MicrocapsulesF-80S, Matsumoto Yushi K.K.).

The heat-expandable microcapsules are heated at 160° C. to make the samefully expand in a mean particle diameter of about 100 μm. Then, apredetermined quantity of expanded microcapsules are added to the vinylacetate emulsion of 5% by weight vinyl acetate concentration based onthe weight of pulp, and ultrasonic waves are applied to the mixture ofthe vinyl acetate emulsion and the expanded microcapsules to dispersethe expanded microcapsules in the vinyl acetate emulsion. Then, themixture and the pulp slurry are mixed to prepare a feedstock. Thefeedstock is dried in a mold by heating at a temperature of 100° C. toform a pulp molding.

An acrylic resin emulsion, a water soluble cellulose derivatives may beused as the binder instead of the vinyl acetate emulsion.

The microcapsules are formed of a thermoplastic resin, such as acopolymer of vinylidene chloride, acrylonitrile and methacrylic ester,and contains an organic solvent (inflating agent) of a low boiling pointin the range of 50° C. to 100° C., such as isobutane, pentene, petroleumother or hexane. The diameter of the heat-expandable microcapsulesbefore expansion is in the range of 10 to 30 μm. When heated at arelatively low temperature in the range of 100° to 150° C. for a shorttime, the heat-expandable microcapsules expand and the expandedmicrocapsules have diameters four to five times those of theheat-expandable microcapsules and volumes fifty to hundred times thoseof the heat-expandable microcapsules. Satisfactory heat-expandablemicrocapsules can be produced by using an optimum quantity of inflatingagent having an optimum boiling point and an optimum construction, andmicrocapsules having an optimum mean particle diameter, an optimumparticle size distribution, optimum elongation and strength under heat,imperviousness to gas and optimum solvent resistance.

General properties and characteristics of the heat-expandablemicrocapsules will be described hereinafter. The heat-expandablemicrocapsules have the appearance of white powder, moisture content of2% or below, a true specific gravity in the range of 0.015 to 0.025, arange of particle size distribution in the range of 30 to 200 μm, a meanparticle size of about 100 μm and a compressive strength of 300 kg/cm²or above, and are formed of a material containing acrylonitrile as aprincipal component.

The true specific gravity of the heat-expandable microcapsules issmaller than that of a conventional filler and the addition of a smallquantity of the heat-expandable microcapsules enables forming alightweight pulp molding. Having the shape of a true sphere, plasticityand elasticity, the heat-expandable microcapsules can be readily mixedin the vehicle and capable of absorbing stress. Since theheat-expandable microcapsules incinerate, only voids can be formed inthe pulp molding, if necessary, by removing the heat-expandable capsulesby sintering. Moreover, the heat-expandable microcapsules has a highheat resistance and their flow temperature is as high as about 130° C.

Measured specific gravities of pulp moldings formed by moldingfeedstocks prepared by the foregoing procedure for different expandedmicrocapsule contents based on pulp are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Content of expanded                                                                            Specific gravity                                             microcapsules (wt. %)                                                                          (g/cm.sup.3)                                                 ______________________________________                                        0                0.83                                                         5                0.54                                                         10               0.45                                                         ______________________________________                                    

As is evident form Table 1, the specific gravity decreases with theincrease of the expanded microcapsule content, which proves that voidsare formed in the pulp moldings by the expanded microcapsules. The pulpmolding containing 10% by weight expanded microcapsules based on pulphas a specific volume about 1.4 times that of the conventional pulpmolding not containing any expanded microcapsules.

Test specimens of the pulp moldings thus formed were subjected tocompression tests to evaluate their static cushioning characteristics.The test specimens were sampled from pulp moldings containing expandedmicrocapsules in contents of 0.5%, 7.5% and 10% by weight, respectively,and a pulp molding containing the expanded microcapsules in a content of10% by weight, and glycerol as a plasticizer. Foam styrene materialhaving a specific gravity of 0.02 was used as a comparative testspecimen. The size of the test specimens is 20 mm×20 mm×10 mm and thetest specimens were compressed at a compression rate of 5 mm/min.

FIGS. 1 and 2 show the measured results of the relation betweencompressive stress and compressive strain for different expandedmicrocapsule contents. As is obvious from FIG. 1, the elastic modulus Eeand the plastic deformation ratio Ep and stress σ for correspondingstrain decrease with increase in the expanded microcapsule content,which proves that the expanded microcapsules improve the cushioningcharacteristics of the pulp moldings. As is obvious from FIG. 2, thecompressive stress for a compressive strain of 25% is reduced by 45% bythe expanded microcapsules contained in a content of 10% by weight, andthe compressive stress of the pulp molding containing 10% by weightexpanded microcapsules is equal to that of the foam styrene material of0.02 in specific gravity. Although the addition of the expandedmicrocapsules in a content of 2% by weight based on pulp is effective onthe improvement of the cushioning characteristics of the pulp moldings,the addition of the expanded microcapsules in a content in the range of5 to 10% by weight will be sufficiently effective.

FIG. 3 illustrates the definition of the elastic modulus Ee and theplastic deformation ratio Ep. In FIG. 3, σ0.25, σ0.50 and σ0.75 arecompressive stresses for compressive strains of 25%, 50% and 75%,respectively.

FIGS. 4 and 5 are typical views of photographs of the test specimentaken before compression and after compression for a compressive strainof 75%, respectively, taken by a SEM (scanning electron microscope). InFIGS. 4 and 5, indicated at 1 is pulp, at 2 are expanded microcapsulesand at 3 are crushed expanded microcapsules. It is known from FIGS. 4and 5 that the compressive deformation of the expanded microcapsules iseffective on the improvement of the cushioning characteristics of thepulp moldings.

Values of Ee, values of Ep, compressive stresses σ0.25 and σ0.50 inducedin the test specimens for different expanded microcapsule contents, andthose of the comparative examples, i.e., the pulp molding containing 10%by weight expanded microcapsules and glycerol, and the foam styrenematerial.

                  TABLE 2                                                         ______________________________________                                        Expanded                                                                      microcapsule                                                                  content   Ee       Ep          Stress (kg/cm.sup.2)                           (wt. %)   (kg/cm.sup.2)                                                                          (kg/cm.sup.2 /%)                                                                          σ0.25                                                                          σ0.50                             ______________________________________                                        0         27.5     13.2        4.8    11.3                                    5.0       23.4     9.4         3.4    6.3                                     7.5       18.8     9.4         3.1    5.9                                     10.0      12.5     8.6         2.5    5.0                                     10.0 and  10.9     7.0         2.2    4.2                                     glycerol                                                                      Foam styrene                                                                            14.9     3.8         2.5    3.1                                     material                                                                      ______________________________________                                    

As is evident from Table 2, when the expanded microcapsule content ofthe pulp moldings is 10% by weight based on pulp, the pulp moldings haveEe and compressive characteristics at σ0.25 substantially equal to thoseof foam styrene material. It is known also from Table 2 that glyceroladded to the pulp molding in a glycerol content of 10% by weight basedon pulp reduces the compressive stress σ0.25 and Ee to values nearlyequal to those for the foam styrene material. Glycerol added to the pulpmolding in a glycerol content of 5% by weight or above based on pulp iseffective and preferable-glycerol content based on pulp is in the rangeof 5 to 50% by weight, because an excessive quantity of glyceroldeteriorates the water resistance of the pulp moldings.

The pulp moldings in the first embodiment were formed by molding thefeedstock containing pulp and the expanded microcapsules. It is alsopossible to form pulp moldings having satisfactory cushioningcharacteristics by molding a feedstock containing pulp and expandablemicrocapsules and heating the pulp molding after molding.

Thus, the pulp moldings in the first embodiment are superior to theconventional pulp moldings in cushioning characteristics, and capable ofsubstituting foam styrene packings and of preventing environmentalpollution.

Second Embodiment

A material for forming pulp moldings in the second embodiment isprepared by dispersing heat-expandable microcapsules formed of anacrylonitrile resin having mean particle diameter of about 100 μm (F-80,Matsumoto Yushi K.K.) by ultrasonic waves in an aqueous solution of abinder containing a predetermined quantity of rosin size (Sizepine E,Arakawa Kagaku Kogyo K.K.) and a predetermined quantity of aluminumsulfate, and mixing the aqueous solution of binder and a pulp slurry of24% by weight solid concentration.

The feedstock was poured in a mold and heated at 100° C. to form pulpmoldings and test specimens were sampled from the pulp moldings.

The moisture absorbing properties of the test specimens were examined.The test specimens of 20 mm×20 mm×10 mm were kept in an environment of atemperature of 60° C. and a relative humidity of 80% for twenty-fourhours. Then, the test specimens were subjected to vacuum drying at 100°C. for about five hours to determined the quantity of water contained inthe test specimens.

Table 3 shows the measured moisture percentage of each test specimen.The heat-expandable microcapsule content of the pulp moldings is 10% byweight based on pulp, and the rosin size content of the same is 2% byweight based on pulp.

                  TABLE 3                                                         ______________________________________                                                            Moisture                                                  Test specimens      percentage (wt. %)                                        ______________________________________                                        Conventional pulp molding (8%                                                                     9.0                                                       Vinyl acetate)                                                                Pure pulp molding (Not                                                                            10.8                                                      containing any binder)                                                        Pulp molding (Containing 10%                                                                      8.9                                                       by weight expanded                                                            microcapsules not containing                                                  any binder)                                                                   Pulp molding (Containing 10%                                                                      5.7                                                       by weight expanded                                                            microcapsules and 2% by                                                       weight rosin size)                                                            ______________________________________                                    

As is obvious from Table 3, the moisture percentage of the pulp moldingcontaining 10% by weight expanded micro-capsules and not containing anybinder is substantially equal to that of the conventional pulp molding,and a small quantity of rosin size, i.e., 2% by weight rosin size,reduces the moisture percentage. A rosin size obtained by processingnatural colophony, in particular, is highly adhesive to pulp and only asmall quantity of rosin size reduces the moisture percentage of the pulpmoldings effectively.

The test specimens were subjected to compression tests, in which therelation between the compressive stress and the compressive strain ofthe test specimens were measured before and after keeping the testspecimens in a humid environment of 60° C. in temperature and 80% inrelative humidity for twenty-four hours. The compression tests provedthat the elastic modulus Ee of the conventional pulp moldings decreasedabout 10% when the conventional pulp moldings were kept in the humidenvironment whereas the elastic modulus Ee of the pulp moldingscontaining the rosin size decreased only 2 to 3%.

Moisture contents of pulp moldings containing the expanded microcapsulesin a content of 10% by weight based on pulp and respectively differingin rosin size content were measured to determine the dependence ofmoisture percentage on the rosin size content. Measured results areshown in Table 4.

                  TABLE 4                                                         ______________________________________                                        Rosin size content (wt. %)                                                                       0     0.5      2.0 5.0                                     Moisture percentage (%)                                                                          8.9   6.4      5.7 5.7                                     ______________________________________                                    

As shown in Table 4, the rosin size contained in a content of 2% byweight in the pulp moldings is sufficiently effective on the reductionof moisture percentage; that is, the moisture percentage of the pulpmolding containing 2% by weight rosin size is as low as 5.7%, which islower than that of the pulp molding not containing the rosin size by35%.

FIG. 6 shows the classification of sizes. Generally, a rosin size isused when an acidic pulp slurry containing aluminum sulfate is used. Anappropriate size is selected taking into consideration the pH(hydrogen-ion activity) of the pulp slurry. As shown in FIG. 6, rosinsizes are produced by synthesis using natural colophony and hence rosinsizes are less pollutive than synthetic vinyl acetate which is generallyused in producing the conventional pulp molding. Since rosin sizes arenot synthetic resins, pulp moldings containing rosin sizes can bedeflocculated in water for reclamation.

The following chemical representation shows the components of rosinobtained from the steam distillation of colophony.

The rosin consists of abietic acid as a principal component, and isomersof abietic acid including parastrinic acid, neoabietic acid andlevopimaric acid. ##STR1##

Methods of producing a rosin size respectively through the production ofmaleic acid and fumaric acid are expressed by the following chemicalformulas. ##STR2##

Thus, the pulp molding in the second embodiment has improved cushioningcharacteristics, the physical properties of the pulp molding will notdeteriorate even if the pulp molding is used in a high-temperature,high-humidity environment, the pulp molding is capable of beingreclaimed and less pollutive than the conventional pulp molding, and thepulp molding is a satisfactory alternative to foam styrene packingmaterials.

Third Embodiment

A feedstock for forming a pulp molding in the third embodiment includesa pulp slurry of 24% in solid content as a principal component, amixture of a vinyl acetate emulsion of 5% by weight vinyl acetatecontent based on pulp and a predetermined quantity of glycerol as abinder, and heat-expandable microcapsules of mean particle diameter ofabout 100 μm formed of an acrylonitrile resin (F-80E, Matsumoto YushiK.K.).

Expanded microcapsules obtained by heating the heat-expandablemicrocapsules are dispensed in the mixture of the vinyl acetate emulsionand glycerol by ultrasonic waves, and then the mixture of the vinylacetate emulsion, glycerol and the expandable microcapsules, and thepulp slurry are mixed to prepare a feedstock. Feedstocks differing fromeach other in glycerol content were prepared. The feedstocks of 10%, 30%and 50% by weight in glycerol content were poured in a mold and dried byheating at a temperature of 100° C. to form pulp moldings. Testspecimens of 20 mm×20 mm×10 mm in size were sampled from the pulpmoldings thus formed, conventional pulp moldings and a foam styreneboard of 0.02 in specific gravity. The test specimens were subjected tocompression tests, in which the test specimens were compressed at acompression rate of 5 mm/min.

FIG. 7 shows the results of the compression tests. As is evident fromFIG. 7, compressive stresses induced in the pulp moldings containing theheat-expandable microcapsules are lower than that induced in theconventional pulp molding. Compressive stress induced in the pulpmoldings containing glycerol as a pulp plasticizer at a high compressivestrain of 75% is relatively small and hence the cushioning effect of thepulp moldings is on the same level as the foam styrene board. Thecompressive stress induced at a compressive strain of 75% in the pulpmolding containing expanded microcapsules of 0.02 in specific gravityand 10% by weight glycerol is smaller than that induced in theconventional pulp molding by 65% and substantially equal to that of thefoam styrene board of 0.02 in specific gravity. Glycerol content of 30%by weight has significant effect on the improvement of cushioningcharacteristics of the pulp moldings in a compressive strain range above25%.

Compressive stresses induced in the pulp moldings of the presentinvention having an expanded microcapsule content of 10% by weight atcompressive strains of 25%, 50% and 75% for different glycerol contentsare shown in comparison with those induced in the comparative examples,namely, the conventional pulp molding and foam styrene board are shownin Table 5 . FIG. 8 is a graph of the relation between strain ε andstress σ, in which σ0.25, σ0.50 and σ0.75 are stresses at strains of25%, 50% and 75%, respectively.

                  TABLE 5                                                         ______________________________________                                                   Glycerol                                                                      content Stress (kg/cm.sup.2)                                       Test specimens                                                                             (wt. %)   σ0.25                                                                            σ0.50                                                                         σ0.75                             ______________________________________                                        Pulp moldings of                                                                            0        3.5      6.6   13.4                                    the invention                                                                              10        2.2      4.8   10.6                                                 30        1.4      2.5   4.8                                                  50        1.1      2.0   4.3                                     Conventional pulp                                                                          --        6.0      14.8  ∞                                 Foam styrene --        2.5      3.2   4.8                                     ______________________________________                                    

As is evident from Table 5, the physical properties of the pulp moldingcan be changed by changing the glycerol content. Preferable glycerolcontent is in the range of 5 to 50% by weight based on pulp because anexcessively large glycerol content reduces the water resistance of thepulp moldings.

The feedstock for forming the pulp moldings of the present invention maybe prepared by mixing the heat-expandable microcapsules and othercomponents of the feedstock instead of preparing the same by mixing theexpanded microcapsules and the other components of the feedstock, andthe heat-expandable microcapsules may be heated to make the same expandafter forming the pulp moldings.

Thus, the pulp molding in the third embodiment has higher cushioningcharacteristics than the conventional pulp molding, is capable ofserving as a packing material alternative to the foam styrene packingmaterials.

Although the invention has been described in its preferred form with acertain degree of particularity, obviously many changes and variationsare possible therein. It is therefore to be understood that the presentinvention may be practiced otherwise than as specifically describedherein without departing from the scope and spirit thereof.

What is claimed is:
 1. A pulp molding composition for forming pulpmoldings comprising a uniformly, dispersed slurry including:pulp fibers;a pulp plasticizer; a binder; and expandable plastic microspherespresent in an amount ranging from approximately 5% to 10% by weight,wherein the pulp molding composition is formable upon exposure to heat.2. The pulp molding composition of claim 1 further comprising a pulpplasticizer.
 3. The pulp molding composition of claim 1 furthercomprising a rosin size and a water soluble polymer binder.
 4. The pulpmolding composition of claim 2 wherein the pulp plasticizer is glycerol.5. The pulp molding composition of claim 1 wherein the binder isselected from the group consisting of chitosan and acrylic resinemulsion.
 6. The pulp molding composition of claim 2 wherein the pulpplasticizer is present in an amount of at least 5% by weight.
 7. A pulpmolding composition for forming pulp moldings comprising a uniformlydispersed slurry including:pulp fibers having a solid concentration of24% by weight; a binder; expandable plastic microspheres present in anamount ranging from approximately 5% to 10% by weight; and a pulpplasticizer, wherein the pulp molding composition is formable uponexposure to heat.
 8. The pulp molding composition of claim 7 furthercomprising a rosin size and a water soluble polymer binder.
 9. The pulpmolding composition of claim 7 wherein the pulp plasticizer is glycerol.10. The pulp molding composition of claim 7 wherein the pulp fibers arerecycled paper.
 11. The pulp molding composition of claim 7 wherein thepulp plasticizer is present in an amount of at least 5% by weight.